Fragile X syndrome is the most common genetic cause of autism, occurring in 1 out of 6000 births. Affected patients also suffer from mental retardation and in some cases seizures. Current treatments involve the use of drugs to ameliorate mood and attention symptoms and to prevent seizures, but are not able to restore normal learning and emotional function. A molecular-level understanding of the neuronal defects in Fragile X syndrome will be necessary for the rational design of therapies to address the underlying cause of the disease. The protein mutated in the disease, the Fragile X mental retardation protein (FMRP), is required for regulating protein synthesis at activated synapses, the communication points between neurons. A large body of evidence suggests that the normal strengthening and weakening of synapses that underlies learning requires the careful regulation of protein synthesis by synaptic activity. Experiments have also suggested a role for FMRP in regulating both synaptic strengthening and weakening. However, the precise relationship between synaptic strengthening and weakening, protein synthesis, and FMRP is poorly understood. For instance, which proteins are synthesized during, utilized in, or required for synaptic strengthening and weakening, and which of these events are affected by FMRP loss, is not known. Research on the function of FMRP in activity-dependent local protein synthesis has been limited by the low sensitivity and resolution of methods for assessing and controlling protein synthesis in living neurons. We have developed new molecular tools that allow the real-time tracking and control of new protein synthesis and the visualization of kinase pathways involved in activity-induced protein synthesis. We propose to use these tools to examine the specificity of protein synthesis responses in synaptic strengthening versus weakening, and to study the effect of FMRP loss on these responses. We will also determine which new proteins are normally required for long-lasting synaptic plasticity, and how FMRP loss might alter those requirements. These studies will provide insight into the regulation and function of synaptic protein synthesis in persistent synaptic plasticity, identify potential molecular targets for therapeutic intervention, and produce new technologies that can benefit the larger neuroscience community. PUBLIC HEALTH RELEVANCE: Current treatments for Fragile X syndrome, the most common genetic cause of autism and mental retardation, are only partially effective in improving mental and neurological function. Our proposal will apply new molecular tools to reveal the molecular bases of the learning and emotional symptoms in Fragile X syndrome. This knowledge will be useful in identifying possible targets for the development of drugs to treat Fragile X syndrome and potentially other autism spectrum diseases.